Certain embodiments of the present invention are directed to integrated circuits. More particularly, some embodiments of the invention provide a system and method for output current regulation. Merely by way of example, some embodiments of the invention have been applied to power conversion systems. But it would be recognized that the invention has a much broader range of applicability.
FIG. 1 is a simplified diagram for a conventional buck power conversion system with primary-side sensing and regulation. The system 100 includes a system controller 102, resistors 118, 164, and 192, capacitors 108, 142, and 124, a power switch 130, an inductor 120, a diode 122, and LEDs 198. In addition, the system controller 102 includes terminals 140, 144, 146, 148 and 154.
An alternating-current (AC) input 110 (e.g., VAC) is provided to input terminals 112 and 114. For example, the system controller 102 receives an input signal related to the AC input 110 and generates a signal 194 to affect the switch 130. When the switch 130 is closed (e.g., being turned on), the inductor 120 is magnetized and a current 190 flows through the switch 130 and the resistor 164. A current sensing signal 106 is detected by the system controller 102 at the terminal 146 (e.g., terminal CS). When the switch 130 is open (e.g., being turned off), the inductor 120 is demagnetized, and a current 192 flows through the diode 122, the capacitor 124, and the LEDs 198. The output current 188 that flows through the LEDs 198 is approximately equal to an average current flowing through the inductor 120. If the average current flowing through the inductor 120 is regulated to a predetermined magnitude, the output current 188 that flows through the LEDs 198 is regulated to be approximately constant at a predetermined magnitude. For example, the output current 188 is estimated by sensing the current 190 through the resistor 164 and calculating a demagnetization period associated with the inductor 120. The terminal 148 is biased at a ground voltage 104. But the conventional power conversion system 100 has some disadvantages.
Hence, it is highly desirable to improve the technique for regulating output currents of power conversion systems.